Data from: Isopycnal mixing suppression by the Antarctic Circumpolar Current and the Southern Ocean Meridional Overturning Circulation

The Meridional Overturning Circulation (MOC) in the Southern Ocean is investigated using hydrographic observations combined with satellite measurements of sea-surface height. A three-dimensional (spatial and vertical) estimate of the isopycnal eddy-diffusivity in the Southern Ocean is obtained using the theory of Ferrari & Nikurashin (2010), that includes the influence of suppression of the diffusivity by the strong, time-mean flows. It is found that the eddy diffusivity is enhanced at depth, reaching a maximum at the “critical layer” near 1000m. The estimate of diffusivity is used with a simple diffusive parameterization to estimate the meridional eddy volume flux. Together with an estimate of the meridional Ekman transport and the eddy volume flux is used to reconstruct the time-mean overturning circulation. By comparing the reconstruction with, and without, suppression of the eddy diffusivity by the mean flow, the influence of the suppression on the overturning is illuminated. It is shown that the suppression of the eddy diffusivity results in a large reduction of interior eddy transports, and a more realistic eddy induced overturning circulation. Finally, a simple conceptual model is used to show that the MOC is influenced not only by the existence of enhanced diffusivity at depth, but also by the details of the vertical structure of the eddy diffusivity, such as the depth of the critical layer.

本研究利用水文观测资料结合卫星海面高度测量数据，对南大洋经向翻转环流（Meridional Overturning Circulation, MOC）展开研究。基于Ferrari与Nikurashin（2010）提出的理论，本研究得到了南大洋等密度面涡动扩散率的三维（空间与垂向）估算结果，该理论纳入了强时均流对扩散率的抑制效应。研究发现，涡动扩散率在深海区域得到增强，并在约1000米附近的"临界层"达到峰值。将所得扩散率估算结果与简单的扩散参数化方案相结合，可估算经向涡动体积输送量。结合经向埃克曼输送量的估算结果与涡动体积输送量，即可重构时均翻转环流。通过对比考虑与不考虑时均流对涡动扩散率抑制效应的两种重构结果，可阐明该抑制效应对翻转环流的影响。研究表明，抑制涡动扩散率会大幅削弱内部涡动输送，并使涡动诱导的翻转环流更贴近实际情况。最后，本研究通过简单概念模型证实，南大洋经向翻转环流（MOC）不仅受深海增强扩散率的影响，同时也受涡动扩散率垂向结构细节（如临界层深度）的调控。